Balancing Formulas

[Britter]

Can someone help me on how to balance formulas?
:oops:

[RobJim]

Well, you basically need to figure out how many copies of each molecule there are on each side such that there are the same numbers of each kind of atom on each side of the equation. Here's an example:

Balance this equation:

C4H10 + O2 => CO2 + H2O

This is a basic combustion reaction. You'll probably see something similar at some point if you haven't already. Count up the atoms on both sides:

Left: Cx4, Hx10, Ox2
Right: Cx1, Hx2, Ox(2+1=3)

Well, to start with, the carbons aren't the same. You know that the same number of carbons should be on both sides, so try multiplying the carbon containing molecule on the right by 4.

C4H10 + O2 => 4 CO2 + H2O

Left: Cx4, Hx10, Ox2
Right: Cx4, Hx2, Ox(8+1=9)

Now, can we multiply the H's on the right without messing up the C's? Yes we can. We multiply the water molecules by 5.

C4H10 + O2 => 4 CO2 + 5 H2O

Left: Cx4, Hx10, Ox2
Right: Cx4, Hx10, Ox(8+5=13)

Now all we have to do is balance the oxygens. However, you can't multiply O2 by anything to get 13. So, try doubling everything so that the 13 becomes an even number and you can find a multiple of O2 that will work.

2 C4H10 + 2 O2 => 8 CO2 + 10 H2O

Left: Cx8, Hx20, Ox4
Right: Cx8, Hx20, Ox(16+10=26)

How many more O2's do you need to make 26? Well, you need 26 total O's, so you need 13 total O2's, and you have 2...so you need 11 more O2's for 13 total.

2 C4H10 + 13 O2 => 8 CO2 + 10 H20

Left: Cx8, Hx20, Ox26
Right: Cx8, Hx20, Ox(16+10=26)

And the equation is balanced.

It's just a process where you make sure the number of atoms on each side is the same.

[charco]

Good clear explanation Rob.

If you'll allow me to add that balancing equations comes from the law of conservation of matter, which says that matter cannot be created nor destroyed in chemical reactions (putting E=mc2 to one side for a moment)

Consequently the particles (atoms) that you begin with in a chemical reaction on the left hand side must appear in the same quantities on the right hand side in the products.

It then becomes a matter of applying simple mathematics to the compounds containing the atoms - remembering that each substance has a formula that cannot be interfered with - balancing numbers must be placed in front of the formulae and multiply ALL of the atoms in the formulae.